The present invention relates to a rack and pinion steering gear and, more particularly, to a rack and pinion steering gear having a low friction yoke assembly.
A known rack and pinion steering gear includes a pinion gear that is rotatably mounted in a housing and is connected with a steering wheel of a vehicle. A rack bar extends through the housing and has opposite end portions connected with steerable vehicle wheels. Gear teeth formed on the rack bar are disposed in meshing engagement with gear teeth on the pinion gear. A yoke assembly is disposed in the housing to support and guide movement of the rack bar relative to the housing. The yoke assembly includes a yoke having an arcuate surface across which the rack bar moves. The support provided by the yoke assembly helps to ensure proper lash between the gear teeth of the rack bar and the gear teeth of the pinion gear.
During operation of this known rack and pinion steering gear, the yoke assembly may be subjected to both heat and high loads. The heat is produced due to friction between the rack bar and the yoke assembly as the rack bar moves across the arcuate surface of the yoke. A high load may occur, for example, when a vehicle hits a pothole in the road surface. The impact load of the vehicle tire with the pothole is transferred to the rack bar through the vehicle tie rods. The rack bar, in turn, transfers a portion of the load to the yoke assembly.
Both heat and high loads may cause a deflection in the yoke assembly. As a result, the yoke assembly may fail to properly support the rack bar and tooth wear on the rack bar and/or on the pinion gear may develop. Thus, a need exists for a low friction yoke assembly that provides sufficient support to the rack bar under high load conditions.
The present invention is a rack and pinion steering gear. The rack and pinion steering gear comprises a housing. A pinion gear is rotatably mounted in the housing. A rack bar is movable relative to the pinion gear. The rack bar has teeth in meshing engagement with teeth of the pinion gear. The rack and pinion steering gear further comprises a yoke assembly in the housing for at least partially supporting and guiding movement of the rack bar relative to the pinion gear. The yoke assembly comprises a yoke and a plurality of rotatable members. The yoke has a first end surface and an axis that extends transverse to the direction of movement of the rack bar. Each of the plurality of rotatable members is supported by the yoke. A portion of each rotatable member projects outward of the first end surface of the yoke for contacting the rack bar. Each rotatable member is rotatable about its axis and is fixed against movement along the yoke axis relative to the yoke.